The trend with time has been to supplant unsightly transmission poles and overhead transmission lines by underground installations. Underground installations improve appearance of a terrain, and improve security.
With the advent of optical fibers, there has been extensive development and planning for the replacement of copper telephone lines, and even some microwave links, with underground optical fiber cables.
Optical fiber cables greatly increase message load capability, can be installed using only a fraction of the space required by existing electrical conduits, and provide room for expansion. In addition to underground installations, optical fiber cables can be installed undersea and, where subsurface installation is impossible or impractical, even replace aerial cables because of lighter weight and reduced bulk.
One of the major advantages of subsurface, i.e., underground and undersea, optical fiber cables, in addition to high message capacity, is that they utilize a totally dielectric construction, and therefore avoid circulating currents. This eliminates the problems caused by electrolytic corrosion, ground loop currents, and the accidental transmission of dangerous voltages from natural sources such as lightning, or manmade sources such as electromagnetic pulses.
To prevent tampering, it is desirable that underground cable installations, such as computer links, be constructed entirely of non-conductive materials to eliminate the possibility of magnetic or electrical detection of their location.
One of the major problems with totally dielectric optical fiber cables is that they are subject to attack by rodents, such as gophers, for subsurface installation; rats and birds, for above-ground installation; and, when placed in undersea locations, fish and sea mammals.
In the past, the solution to the problem has been the use of metallic armor. However, this cancels the advantage of dielectric optical fiber cables and increases weight, cost and corrosion problems.
The purpose of this invention is, therefore, directed to the development of high-strength optical fiber cables which resist attack by rodents, fowl and fish.